Autism spectrum disorders (ASDs) are among the most common childhood neurodevelopmental syndromes. A fundamental goal in the field is the discovery of methods that mitigate core autism symptoms. Greater severity of autism symptoms is associated with increased functional impairment, while lower levels of symptoms are associated with better prognosis. Core autism symptoms span from social-cognitive impairments, to pragmatic language deficits, to repetitive and rigid behaviors. The core symptoms tend to be stable and resistant to intervention. While behavioral and talk-based therapies are common for school-aged youth with ASD, with the average child using about $6,000 of outpatient services annually, the current evidence base is weak. Most treatments involve group-based social skills training, with limited external validity and durability of effect. No psychosocial treatment for core autism symptoms in school-aged children with ASD meets American Psychological Association guidelines for possible efficacy. Cognitive behavioral therapy (CBT) offers a novel approach for addressing core autism symptoms in higher functioning school-age youngsters. CBT has been successfully adapted to treat emotional problems in school-aged children with ASD (e.g., Wood et al., 2009a). Initial results suggest that CBT may also be promising for reducing core autism symptoms (Wood et al., 2009b; Drahota, Wood et al., 2011). The treatment is based on a contemporary model of memory retrieval competition, employing strategies for enhancing the retention of adaptive conceptual and behavioral responses and the suppression of idiosyncratic beliefs and behaviors in daily social contexts (e.g., school, home), emphasizing the use of deep semantic processing to enhance memory retrieval. We are proposing a randomized controlled trial to examine the efficacy of CBT relative to the standard of care in the community, social skills training (SST), in youngsters with ASD. The CBT program has been tailored over the last five years to the characteristics and clinical needs of high-functioning youth with ASD. In response to the 2009 Interagency Autism Coordinating Committee (IACC) Strategic Plan, a modular treatment approach is employed to personalize the intervention. The primary outcome measure is the Playground Observation of Peer Engagement scale, an independent evaluator-rated school playground observational measure of joint engagement, which is a psychometrically valid measure of core autism symptoms with established treatment sensitivity. The proposed research will (1) examine the short term efficacy of CBT relative to SST on autism symptom severity, (2) evaluate the durability of observed treatment gains in CBT responders, (3) cross-validate the ADOS, ADI-R, and SRS as measures of treatment outcome against the primary outcome measure (school observations of joint engagement), and (4) identify predictors of treatment outcome. A total of 80 youth (ages 7-12 years) with ASD will be randomly assigned to CBT or SST. Given the lack of evidence-based treatments for core autism symptoms in the school age-group, positive findings from this trial could have considerable public health significance.